The goal of the proposed investigation is to determine whether immunologic factors contribute to resistance to HIV infection in high- risk seronegative subjects. We hypothesize that an anti-HIV immune response may confer protection to HIV infection in exposed individuals. We will obtain inguinal lymph node biopsies and PBMC specimens from high- risk homosexual men who have had recent exposure to HIV as a result of unprotected receptive anal intercourse. We anticipate that specific anti-HIV cellular immune responses will be detected in the inguinal nodes and that these responses will be higher than those in the peripheral blood. The inguinal nodes, which drain the lower rectum and anus, are likely to be among the first tissue sites exposed to HIV after rectal inoculation, and these nodes are easily accessible for biopsy. Specific anti-HIV memory T cell immune responses will be measured in assays for IL-2 production in response to synthetic HIV envelope peptides and in assays for precursors of cytotoxic T cells stimulated in response to HIV proteins expressed by recombinant vaccinia viruses. Suppression of HIV replication by a soluble factor produced by CD8+ cells will be evaluated as a further measure of cellular immunity. Negative controls for all the studies will be inguinal lymph nodes and blood from heterosexual men who are not at risk for exposure to HIV and who are undergoing hernia repair. By studying subjects with past as well as recent exposure and subjects who had high risk behavior at the beginning of the epidemic in 1984 but have no recent behavioral risk, we will determine whether exposure in the past led to a sustained response, i.e., long-term immunologic memory to HIV. In collaboration with Dr. Ashley Haase, we will also investigate whether viral nucleic acid can be detected in the nodes using in situ DNA and RNA hybridization. Nested DNA PCR on lymphoid cells and PBMC will also be performed to determine whether any viral sequences can be detected. These studies have important implications with regard to HIV vaccine development. They will provide evidence for or against the hypothesis that humans can be exposed to enough viral protein in the context of natural exposure to mount a long-lasting immune response in the absence of a disseminated infection. This knowledge is critical to understand immune control of lentivirus infection in humans.